Size Matters: Sometimes Larger is Better
Large canopy trees provide shade for cooling you and your plants. Smaller trees and shrubs layered in can add to this cooling effect.
By Jan Scow
In our previous blog post (Size Matters: Small is Better!) we discussed why it is beneficial to plant nursery trees in smaller containers. Yes, in the beginning, it is best to start out with trees that are small and have only been in the nursery for a short while. But it is also most beneficial to plant trees that will become large as they mature.
There are many benefits of trees in urban areas, including cooling, shade, capture of air pollutants, carbon sequestration, reduced crime, etc. In general, the larger the tree the more benefits it provides. So, not all trees are created equal as far as their environmental benefits. Some trees grow fast and get large quickly, providing more environmental benefits sooner. Some trees grow more slowly but will eventually get large. These trees will provide many benefits as well, but it will take longer for those benefits to accrue. Some trees are small at maturity or have limited benefits for other reasons.
If we look at the benefits of shade it becomes readily apparent that size and canopy structure are important factors. Some trees provide very dense shade. A good example of this is the mulberry tree which creates a solid canopy of densely packed leaves with little sunshine penetrating through the canopy. Another example would be the coast live oak, especially if they are not excessively pruned.
Some trees provide very little shade and are far less beneficial. In Ojai we are seeing a lot of Palo Verde trees being planted. While these are attractive drought tolerant trees, they are small trees with a very open canopy and create virtually no shade; their benefit is quite minimal ( they are far better as an accent tree). Another good example is palm trees. Most palm trees provide very limited shade due to the small canopy they have. And there’s the crape myrtle tree. Again, this is a small tree, which grows very slowly and has a fairly open canopy producing limited shade.
Of course, there are other considerations when choosing a tree. You shouldn’t plant a large growing tree in a small space, or a tall tree under power lines for example. But, in general, larger growing trees with denser canopies provide more environmental benefits than smaller trees or trees with open canopies.
Jan is a Registered Consulting Arborist and a Board Certified Master Arborist on the Ojai Trees Board of Directors.
A mature Palo Verde Tree will cast only light shade.
A mature Mulberry tree provides lush shade underneath its branches.